Differences between abstract class and concrete class in Java

Java Object Oriented Programming Programming

In Java, abstraction is achieved using Abstract classes and interfaces. An abstract class contains abstract methods which a child class. Following are the important differences between abstract class and a concrete class.

Sr. No.	Key	Abstract Class	Concrete Class
1	Supported Methods	Abstract class can have both an abstract as well as concrete methods.	A concrete class can only have concrete methods. Even a single abstract method makes the class abstract.
2	Instantiation	Abstract class can not be instantiated using new keyword.	Concrete class can be instantiated using new keyword.
3	Abstract method	Abstract class may or may not have abstract methods.	Concrete clas can not have an abstract method.
4	Final	Abstract class can not be declared as a final class.	Concrete class can be declared final.
5	Keyword	Abstract class declared using abstract keyword.	Concrete class is not having abstract keyword during declaration.
6	Inheritance	Abstract class can inherit another class using extends keyword and implement an interface.	Interface can inherit only an inteface.
7	Interface	Abstract class can not implement an interface alone. A child class is needed to be able to use the interface for instantiation.	Interface can be implemented easily.

Example of Abstract Class vs Concrete Class

JavaTester.java

public class JavaTester {
   public static void main(String args[]) {
      Cat lion = new Lion();
      lion.eat();
   }
}
abstract class Cat {
   abstract public void eat();
}
class Lion extends Cat{
   public void eat(){
      System.out.println("Lion eats");
   }
}